The present invention relates to a cooling technique for a gas turbine plant including a compressor, gas turbine, and combustor, and more particularly, to a gas turbine plant including an improved combustor.
Referring now to FIGS. 1 and 2, there is shown a conventional gas turbine plant that uses air as its cooling medium. In FIG. 1, compressed air 11 compressed by means of a compressor 10 is guided to a combustor 12, whereupon it is burned together with a fuel to form a combustion gas 16. The gas 16 is fed to a gas turbine 13 to drive it.
The wall of the combustor 12, which is exposed to high temperature, is cooled by introducing some of the compressed air 11 as cooling air 6 into the combustor 12. FIG. 2 shows a wall cooling structure for the combustor 12. A wall 1 of the combustor 12 is of a dual structure having a space therein. A large number of passages are divided by partition walls in this space.
The cooling air 6 introduced through a large number of cooling air inlet ports 2a in the outer surface of the combustor wall 1 passes through the passages that are divided by the partition walls, thereby effecting impact jet cooling 12a and convection cooling 12b. As the air 6 is discharged into the combustion gas 16 through cooling air outlet ports 3a after cooling the combustor wall 1 in this manner, its subject the combustion gas side of the combustor wall 1 to film-cooling 12c.
Referring now to FIGS. 3 and 4, a gas turbine plant using steam or some other cooling medium will be described. In order to improve the thermal efficiency of modern gas turbines, the combustor wall is subjected to impact jet cooling and convection cooling with use of steam, which has a high cooling effect, in place of air. This cooling medium may be discharged into the combustion gas or recovered entirely.
FIG. 3 is a cooling system diagram showing an example of the gas turbine plant that uses steam as its cooling medium. As shown in FIG. 3, a cooling medium 7 is supplied by means of a cooling medium supplier 15, which utilizes the power or waste heat of a gas turbine. Accordingly, the medium 7 cannot be supplied when the gas turbine is activated. Before the supply conditions of the supplier 15 are settled, therefore, the cooling medium 7 is supplied by means of an auxiliary cooling medium supplier 17. When the conditions of the supplier 15 are settled, thereafter, the auxiliary supplier 17 is switched over to the supplier 15 by means of a cooling medium changer 18, and the supply of the cooling medium 7 is continued. FIG. 4 shows an example of a combustor wall cooling structure. In this example, the entire cooling medium (steam) is recovered.
The cooling medium 7 supplied from the supplier 15 or the auxiliary supplier 17 is introduced through a cooling medium supply header 8. The supply header 8, which has a cooling medium passage therein, is provided on one side portion of the outer surface of a dual-structure combustor wall 1. The medium 7 flows into the passage through cooling medium inlet ports 4, thereby subjecting the wall 1 to impact jet cooling and convection cooling. Thereafter, the medium 7 is recovered through cooling medium outlet ports 5 by means of a cooling medium recovery header 9. The cooling medium passage, which includes a space in the double-wall structure, is provided over the combustor wall 1 inside the supply header 8. The outlet ports 5 are formed in the other side portion of the outer surface of the wall 1.
In the case where air compressed by means of the compressor is used for cooling, as shown in FIGS. 1 and 2, a predetermined turbine inlet temperature can be obtained only by previously increasing the combustion gas temperature by a margin corresponding to a gas temperature drop that is caused as the cooling air is discharged into the combustion gas after the combustor is cooled, as shown in FIG. 5. Since the rise of the combustion gas temperature causes the delivery of NO.sub.X gas to increase exponentially, it constitutes a hindrance to the development of low-NO.sub.X gas turbine plants.
In the case where steam is used as the cooling medium 7 for cooling the combustor wall 1, the cooling medium may be discharged into the combustion gas 16. As in the aforesaid case of the air-cooling system, therefore, the combustion gas temperature must be increased, so that the delivery of NO.sub.X increases inevitably.
When the cooling medium 7 is recovered, moreover, the cooling medium supplier 15 is used that utilizes the power or waste heat of the gas turbine, as shown in FIG. 3. Accordingly, activating the gas turbine separately requires use of the auxiliary cooling medium supplier 17. Besides, in this case, the cooling medium changer 18 must be used to replace the two suppliers 15 and 17 with each other.